This website offers free resources for applicants on a number of different topics including personal statements, applications, LSAT, etc...

Here is an excerpt from the Personal Statement section (for more click the link above):

Your personal statement is your opportunity to give law schools a reason to say "yes" to your file. Don't be afraid to take risks in it. Remember that a mediocre personal statement is wasted paper in your file.

What does a law school look for in a personal statement? First of all, good writing; anything less than perfection counts as a negative. Secondly, the admissions officer is looking for diversity. Any information you wish to provide about ethnic or socioeconomic background is most likely to appear here. Any personal obstacles you've had to overcome will also be addressed here. To the extent that you're not the "mainstream applicant," this is your chance to show it.

Beyond these two factors, answers varied somewhat from school to school. Many admissions officers stressed that this is your opportunity to address any weaknesses in your file. Some said they look for leadership, others for community involvement, still others for maturity and seriousness in applying to law school. Many look for "what makes you unique," your diversity in more personal terms; it could be an Olympic medal or your skills as a gourmet cook, nature photographer or quilt-maker. Many schools also look for "personal growth and development," a category which frequently overlaps the one above.

The best overall instruction I've seen comes from U. Wisconsin's application:

"Don't be afraid to talk to us about an unusual experience. It is often these experiences, and your recounting of them, that can speak volumes to us about you, your level of self-reflection, your imagination, how you understand and engage the world around you, and what you could bring to the Law School. We also encourage you to write your personal statement in a narrative tone so that more of your personality and who you are comes through in the writing. You should envision the personal statement as your opportunity to have a "conversation" with the Admissions Committee...."